Energetic Ions in the High Latitude Boundary Layer of the Magnetosphere – RAPID/Cluster Observation
Q.-G. Zong1, T. A. Fritz1, B. Wilken2, and P. Daly2
1 Center for Space Physics, Boston University, Boston, MA, USA
2 Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany
In Solar-Terrestrial Magnetic Activity and Space Environment, edited by Wang and Xu, COSPAR Colloquia, Series, Vol. 14, pp359-364, 2002.
The RAPID/CLUSTER is an advanced ion spectrometer with a position sensitive time-of-flight (T) and energy (E) detection system which determines the mass of incident energetic ions. The energy range extends from 50 to 1500 keV. Combined with the sectored spin plane of the spacecraft it allows the imaging of flux distributions over the complete unit sphere (4π) in phase space. The thrust of this paper concentrates on the energetic ion events near the high latitude boundary layer of the magnetosphere during both IMF southward and northward conditions. On December 19, 2000, an energetic ion layer has been observed in the high latitude boundary region just outside the magnetosphere during IMF southward. However, on January 14, 2001 for an IMF northward case, layer-like energetic ions have been observed inside the magnetosphere. The energetic particles for both cases are hightly anisotropic, but exhibit a clear sunward or antisunward flow while geomagnetic activity is very quiet. The flow directions for both the IMF northward and southward case can be explained in a framework of convection models — dayside reconnection occurred in the subsolar region during a southward IMF Bz; high latitude reconnection happened during IMF northward. The reconnection processes are important simply because they either open a path for energetic magnetosphereic ions to escape into the magnetosheath (Southward IMF), or to provide a reverse convection geometry (Northward IMF) rather than by particle acceleration. The origin of the observed energetic particles for both cases in the high latitude boundary region is undetermined but may be provided by the tail plasma sheet particles because of a minimum magnetic field existing off equator in the high latitude region of the magnetosphere (e.g. Tsyganenko magnetic field model). In this way, particles initially mirroring near the equator are expelled from low latitudes and subsequently are swepted into the boundary layer at high latitudes.